The present invention relates to the detection and monitoring of electrical shorts in synchronous machine field windings and, in particular, automatically identifying and tracking electrical shorts in the field windings of rotors.
The field windings in the rotor of a generator are generally an annular array of conductive coil bars arranged in slots around the outer periphery of the rotor. The coils extend longitudinally along the length of the rotor and are connected by end turns at each end of the rotor. A connected pair of coil bars and end turns form a coil winding turn.
A rotor has multiple poles, e.g. two, four or six poles. Several coil winding turns are arranged on a rotor to form a pole. An exciter circuit applies DC (direct current) to the coil bars of the rotor.
Shorts may develop in the field windings. For example, the insulation separating the conductor bars or end turns may break down and cause an electrical short across one or more coils in the field winding. The shorts in the coil windings are referred to as shorted turns.
A short in a field winding may cause a variety of overheating conditions and related vibration problems. Identification of shorted turns in a timely and cost-effective manner is desirable to reduce the off-line downtime period needed to repair shorts in the coil windings of the generator.
Shorts may be detected by analyzing the magnetic flux generated by the field windings. A flux probe sensor is introduced in the air-gap between the rotor and stator to monitor the flux from the field windings of the rotor. The sensor generates a signal proportional to the rate of change of the electromagnetic flux in the air-gap.
A system for flagging shorted turns in the coil windings of a generator is disclosed in U.S. Pat. No. 6,911,838, ('838 patent) entitled “Online Detection Of Shorted Turns In A Generator Field Winding” and assigned to the General Electric Company. The system '838 patent teaches an automated technique to analyze magnetic flux data captured from the rotor and flag the captured flux data likely to be indicative of a shorted coil.